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Old 23rd March 2015, 10:15 PM   #1
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Default help improving cheap QFX wireless mic

Though I'd like to have one, I just can't afford a good wireless mic. But having found a QFX model M-309 wireless mic brand new for $24, I figured I'd see if it might at least be hacked into being usable. Surprisingly, it forms a pretty quiet connection, so from a radio point of view its usable. The big problem is the cheap mic element. It overloads easily if its positioned close to your mouth or you sing loud. I figured the electronic input stage was being overloaded, but I figured I'd start at the mic, and put a scope right across its output, while in circuit. I was surprised to see that when a spoke loudly into it, the output from the raw mic itself was over 2V p-p, and was obviously clipping (probably mechanically clipping). For such a high voltage I assumed I was looking at a ceramic mic element, but since it doesn't output anything without being connected to the transmitter (there's about 7VDC there, maybe its just a high output condenser mic?

In any case, aside from it not being a very directional mic (breath from my nose is picked up way too much), I'm sure i could make it closer to 'usable" if I could figure a way to make the mic element less sensitive. If I take off the foam windscreen and put duct tape over its holes, then its very attenuated and won't distort. But of course then it sounds like you're talking from inside a barrel . I might consider investing in a better mic element if I knew for sure what kind of element it was, but for now can anyone think of a way to acoustically attenuate the response of the mic in such a way that it loses sensitivity to all frequencies approximately the same? remeber... its not the electrical output I need to attenuate... its the mic's raw acoustic sensitivity.

Thanks for any creative thoughts!
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Old 23rd March 2015, 10:20 PM   #2
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All I can suggest is connect a Shure mic to it instead of the cheap electret mic?
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Old 23rd March 2015, 11:30 PM   #3
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Quote:
Originally Posted by JonSnell Electronic View Post
All I can suggest is connect a Shure mic to it instead of the cheap electret mic?
Well I didn't have anything that good to test with, but I think I got lucky! I had another small electret mic I saved from something... possibly a built in mic from an old cassette recorder. Glad i saved it! It was much less sensitive and much better sounding too. It was just slightly larger, but no so large I couldn't hack it in to the original enclosure (see photos). Because its way less sensitive, I can adjust it closer to my mouth and it won't overload, and also doesn't pick up jets of air from my nose as badly.

In any case, its still a long way from a high end system, but its at least usable now.

original disassembled mic, with my better element next to it...
Click the image to open in full size.

Substituted element...
Click the image to open in full size.

A little Duct tape since it didn't fit quite as well...
Click the image to open in full size.

And re-assembled.

Click the image to open in full size.

Hopefully other musicians on a low budget will benefit from this discussion. This device has now been improved 500%!! I suspect the issue is that the manufacturer used the same mic element for the lapel mic as he did for the head version. A lapel mic would need the extra sensitivity, but for the head version it wasn't a good pick.
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